Because smart-phones are in wide use, biometric authentication has attracted substantial attention as a user authentication technology for them. Voice is one of the most promising biometric modalities for user authentication on smart-phones because a user interface involving a microphone is commonly used on such devices and because biometric-specific sensors are not necessary. However, biometric authentication requires template-protection technologies to enhance the security of the biometric template that stores a user’s biometric information. Therefore, to design a more secure and convenient template-protection method for smart-phones, we propose a method to generate biometric bit strings from text-independent voice data. We demonstrated its effectiveness through simulation experiments.